Impedance spectroscopy is a promising method for tissue ischemia measurement, because it is non-invasive and suitable for long-term continuous monitoring. Ischemia causes biochemical and physiological changes in tissue which influence the tissue impedance. These changes can be detected by impedance spectroscopic measurements. To fully develop this method, the authors first constructed a dedicated instrument impedance spectrometer, and then used it to experimentally investigate the relationships between ischemia and tissue impedance. Results from in-vivo animal experiments indicate that the relationships between tissue impedance and ischemia is complex and nonlinear. In order to quantitatively describe this relationship, the authors used artificial neural networks to develop an algorithm for predicting tissue pH based on measured complex tissue impedance (tissue pH is the best known quantitative estimator of the ischemia levels). Preliminary experimental results show a good correlation (&ap;95%) between the predicted and actual ischemia levels (expressed in pH). The achieved correlation level is not yet sufficient to provide for accurate measurements of tissue pH